Holding plate for electroplating a detonator plug



Dec. 14, 1965 D. D. TAYLOR 3,223,599

G LA IN PLATE FOR ELEGTROP T Filed April 15, 1965 INVENTOR. 3O 4 OHN/'L DW/GHT TAYLOR 5) HIS HTTORNEYS. HARRIS, KIEcH, RUSSELL 6; KERN United States Patent Ofifice 3,223,599 Patented Dec. 14, 1965 3,223,599 HOLDING PLATE FOR ELECTROPLATING A DETONATOR PLUG Daniel Dwight Taylor, Altadena, Caliii, assignor to Beckman Instruments, Inc., a corporation of California Filed Apr. 15, 1963, Ser. No. 273,198 4 Claims. (Cl. 204) This invention relates to electrical detonators and more specifically to the manufacture of detonator plugs and to an improved structure.

In one manner of manufacture of detonator plugs, a plug disc of very small dimension is drilled to accept a plastic coated wire or stem. The drilled hole is somewhat oversized. A typical procedure is described in copending patent application Serial No. 147,354, now Patent No. 3,155,553, filed October 24, 1961. Taylor and Brawner. As a result of the drilling step, a burr appears by one face of the plug disc about the drilled hole. The burr is preferably not removed at this time because of the possibility of returning part of the burr inside of the hole where it would interfere with assembly. Following the drilling of the hole in the plug disc; a slightly undersized plastic coated wire or stem is positioned within the hole of the plug disc. The plastic coating is capable of withstanding fracture upon the subsequent application of high swaging force to the plug disc. The detonator plug, i.e., the plug disc with the coated wire therein, is positioned within a suitable bushing fixture which closely controls the outside diameter and finish of the completed plug upon application of a high swaging force, generally in the range of 3,000 to 5,000 pounds, to the end of the plug. In a subsequent operation, the burr and the wire or stern adjoining the burr are ground off to provide a substantially smooth head for the detonator plug. This grinding operation removes a thin oxide film which is characteristic of stainless steel out of which the plug is desirably made. The detonator plug at this time is placed directly in a gold-plating bath and a thin gold coating is formed on the recently ground head. The gold coating forestalls the formation of an invisible oxidation film on the head which would interfere with firing of the detonator.

It is conventional practice during the finishing operations of grinding and gold-plating the face to hold a large number of detonator plugs in a fixture. Heretofore, the method of holding the detonator plugs or buttons, as they are sometimes called, involved inserting the stem or wire of the detonator plug in a hole of the fixture and then pouring a low-melting alloy around the wire which on freezing held the detonator plug for the subsequent operations of grinding and gold-plating. The later removal of the detonator plug from the grip of the alloy presents serious problems. If the alloy is melted and allowed to run away from the wire, it is not possible to obtain a clean surface and the residue of the alloy has to be picked off with a needle by hand. This, it will be appreciated, is a very tedious task and it has also proven difficult to accomplish without damage to the plastic coating. An alternative procedure involves gripping the edges of a finished detonator plug between the jaws of cutting pliers and pulling the detonator plug out of the solid alloy. With this method of removal unknown damage may be imparted to the plug, especially at the swaged joint. The invisible damage will become known only when an attempt is made to fire the detonator employing the plug.

It is a object of this invention to provide an improved method of manufacturing a detonator plug.

A still further object of the invention is to provide an improved fixture for holding a plurality of detonator plugs during the finishing steps of grinding and electroplating.

A still further object of the invention is to provide a detonator plug of a novel structure which facilitates the finishing operations. These and other objects and advantages of the invention will become more apparent in the following detailed description of a preferred practice of the invention and as illustrated in the accompanying drawing.

In the drawing:

FIG. 1 is a sectional view of a detonator plug of the invention following application of swaging force to neck down an electrode wire placed in the hole of the plug disc the view illustrating an intermediate stage of fabrication;

FIG. 2 is a fragmentary sectional view showing two detonator plugs held within a fixture of the invention;

FIG. 3 is a sectional view illustrating the detonator plug in an advanced stage of fabrication, following grinding of the head and prior to electroplating;

FIG. 4 is a plan view of the head of the detonator plug of FIG. 3;

FIG. 5 is a sectional view of a finished detonator plug following gold-plating; and

FIG. 6 is a plan view of the detonator plug of FIG. 5.

The detonator plug 10 of the invention comprises a plug disc 12 which is swaged about a wire or stem 14. The plug disc 12 is preferably a punched slug of Type 302 stainless steel which is drilled to accept the wire 14. The wire 14 has a plastic coating 16 which is capable of withstanding fracture upon application of high swaging force. The drilled hole of the plug disc 12 is oversized and it will be seen that a burr 18 appears on one face of the plug disc (see FIG. 1). Following the drilling of the hole in the plug disc 12, the slightly undersized coated wire 14 is positioned within the hole of the plug disc. In the practice of the invention, one end of the wire 14 has been threaded. For a detonator plug employing a wire stem of 0.062 inch diameter, threads per inch have been found to be suitable.

The plug disc 12 with the coated wire 14 therein is positioned within a suitable bushing fixture which limits the outside diameter and imparts a finish to the completed disc plug upon application of a high swaging force. The swaging force is applied through a doughnut-shaped die to the end of the plug opposite the burr 18. This high swaging force brings about an inward fiow of metal toward the hole of the plug disc 12, resulting in the necking down of the wire 14 which as seen in FIG. 1 secures the wire within the disc plug. Simultaneously with the inward flow of metal there is an outward flow of metal to give the diametrical dimension and finished surface of the completed plug. The detonator plug of FIG. 1 illustrates the disc plug 12 immediately subsequent to the swaging operation. The plug is then ejected from the fixture bushing by a plunger. The tough plastic coating of the wire plug, which is preferably made from the plastic Formvar, transmits the high pressure without fracturing.

In the practice of the invention, the detonator plug 10 at the stage of manufacture illustrated in FIG. 1 is then held to a holding plate 22 of a fixture 20 by an elongated nut 24. In actual practice the fixture 20 is usually designed to contain detonator plugs 10. The fixture 20 with the several detonator plugs 10 fastened thereto is conveniently presented to an abrasive wheel to grind ofi the burrs 18 and protruding portions 28 (see FIG. 1) of the wires 14. Ordinarily a series of abrasive papers will be used in the grinding operation with the last grinding being achieved with a 600-grade Carborundurn. This grinding operation also removes a thin surface film which is characteristic of stainless steel. In order to avoid or forestall the formation of an invisible oxide film which would present an electrical resistance, the recently ground face 30 of the disc plug 12 is desirably provided with a gold-plated face 43. It has been found that stainless steel plugs allowed to stand for several hours in air before assembly without the gold-plated face often produce unsatisfactory firings. Since the holding plate 22 of the fixture 20 is desirably made of steel or copper, it may be used as one of the terminals of an electroplating bath.

There is an additional advantage in the use of the fixture 20 of the invention as one of the terminals of the electroplating bath. Heretofore, when a fixture having the detonating plugs held thereto by a low-melting alloy was used, oftentimes there would occur a poisoning of the gold-plating bath by the low-melting alloy, resulting in an unduly short life for the plating bath.

The metal holding plate 22 of the fixture 20 has a plurality of transverse holes 34, each comprising a first section 36 of smaller diameter in alignment with a second section 38 of larger diameter. The end wall 40 of the larger second section 38, which is located at the juncture of the second section with the first section, has desirably a conical shape. The elongated nut 24 has a rounded or ball-shaped end 44, which on engagement with the conical end wall 40 presents a circular line contact rather than a surface contact which would occur with complementary surfaces. It has been found that a line engagement of the end wall 40 and nut 24 allows for some nonperpendicularity of wire 14 as to the plug 10 and still assures the holding of the inside face of the plug 10 flush against the fixture holding plate 22.

Where the manner of manufacture consistently produces the detonator plugs 10 with the wires 14 normal to the disc 12, the end wall 40 of the larger second section 38 may have a rounded surface which is complementary to the ball-shaped end 44 of the elongated nut 24. In another form, the end wall 49 of the second section 38 and end 44 of the nut may be provided with conical complementary surfaces. In the latter two forms, the contact between the hole and nut is a surface contact, in contrast to the line contact illustrated in FIG. 2.

It will be seen that the nut 24 has an outside diameter somewhat less than the diameter of the second section 38 of the transverse hole 34 of the holding plate 22. The nut is provided with a wrench-receiving head 46, usually hexagonal in configuration, at the end opposite the rounded or ball-shaped end 44. The nut is internally threaded along its longitudinal axis.

The detonator plug 10 is held to the holding plate 22 with the face of the plug disc 12 engaging the holding plate about the transverse hole 34 and with the stem 14 of the plug extending through the first section 36 into the second section 38 of the hole. The portion of the elongated nut 24 within the second section 38 engages the threads of the plug stem 14 to draw the plug disc 12 against the holding plate 22, thereby bringing about bottoming of the ball-shaped end 44 of the nut 24 against the conical end Wall 40 of the second section 38 of the transverse hole. The provision of the conical end wall '40 and the ball-shaped end of the elongated nut 24 assures proper alignment of the detonating plug within the fixture 20.

The gold-plated detonator plug 10 of the invention is illustrated in FIGS. and 6. It will be seen that the very thin gold-plate 43 does not form on the exposed surface of the plastic coating 16, thus maintaining the insulation between the wire 14 and the disc 12.

With the fixture of the invention it is possible to mount considerably more detonating plugs than was formerly possible with a fixture using a low-melting alloy to anchor the plugs in place. With a detonating plug having a disc plug diameter of approximately .175 inch diameter, it has been found that a torque of 5 to 7 oz./in. is best employed for seating the nut within the second section 38 of the transverse hole and in drawing the plug disc 12 tight against the face of the fixture 20.

Although exemplary embodiments of the invention have been disclosed herein for purposes of illustration, it will be understood that various changes, modifications, and substitutions may be incorporated in such embodiment without departing from the spirit of the invention as defined by the claims which follow:

1. In combination:

a metal hold'mg plate having a transverse hole including a first section of smaller diameter and a second section of larger diameter;

a detonating plug structure comprising a conductive plug disc and a conductive stem securely held within a central hole of the disc and extending outwardly from one face of said disc, said stem being insulated from the plug disc and provided with threads along at least a part of its external length;

a nut having an outside diameter somewhat less than the diameter of the second section of the hole of the holding plate; and

said plug structure being held to the holding plate with a face of the plug disc engaging the holding plate about the transverse hole and with the stem extending through the first section and into the second section of the hole, said nut engaging threads of the stem to draw the plug disc against the holding plate and to bottom the nut against the end wall of the second section at the juncture of the second section with the first section of said transverse hole.

2. A combination in accordance with claim 1 wherein the inner end of the nut is rounded to form a line engagement with the end wall of the second section which end wall has a conical shape.

3. In a method for the electroplating of a conductive detonator plug comprising a plug disc and a stem of smaller diameter extending outwardly from one face thereof along the axis of said plug disc, the step comprising:

providing as one terminal of an electroplating bath a metal holding plate having a transverse hole of two succeeding diameters, holding the detonator plug to the holding plate with a face of the plug disc engaging the holding plate about the transverse hole and with the stem extending through the smaller diameter length of the hole into the larger diameter length of said hole, engaging an elongated nut to the threads of the plug stem, drawing the plug disc against the holding plate and bottoming the nut against the wall at the juncture of the two diameter lengths of the transverse hole, placing the plate in an electroplating bath and electroplating the exposed portions of said plug.

4. In a method for electroplating a conductive detonator plug comprising a plug disc and a stem of smaller diameter extending outwardly from one face thereof along the axis of said plug disc, the step comprising:

providing as one terminal of an electroplating bath a metal holding plate having a transverse hole of two succeeding diameters, holding the detonator plug to the holding plate with the face of the plug disc engaging the holding plate about the transverse hole and with the stem extending through the smaller diameter length of the hole into the larger diameter length of said hole, engaging an elongated nut having a portion of its length exposed outside of the holding plate and being provided on said exposed section witha wrench receiving head to threads of the plug stem, drawing the plug disc against the holding plate and bottoming a rounded end of the nut against a conical end Wall atthe juncture of thetwo diameter lengths of the transverse hole, placing the plate in References Cited by the Examiner UNITED STATES PATENTS Robe 204-297 Van Tuyl 86-1 Heller 85-32 Allen 85-32 Russell 204-46 Belke 204-297 Hay 86-1 Goellner 174-151 Divers 174-151 BENJAMIN A. BORCHELT, Primary Examiner.

SAMUEL W. ENGLE, Examiner. 

3. IN A METHOD FOR THE ELECTROPLATING OF A CONDUCTIVE DETONATOR PLUG COMPRISING A PLUG DISC AND A STEM OF SMALLER DIAMETER EXTENDING OUTWARDLY FROM ONE FACE THEREOF ALONG THE AXIS OF SAID PLUG DISC, THE STEP COMPRISING: PROVIDING AS ONE TERMINAL OF AN ELECTROPLATING BATH A METAL HOLDING PLATE HAVING A TRANSVERSE HOLE OF TWO SUCCEEDING DIAMETERS, HOLDING THE DETONATOR PLUG TO THE HOLDING PLATE WITH A FACE OF THE PLUG DISC ENGAGING THE HOLDING PLATE ABOUT THE TRANSVERSE HOLE AND WITH THE STEM EXTENDING THROUGH THE SMALLER DIAMETER LENGTH OF THE HOLE INTO THE LARGER DIAMETER LENGTH OF SAID HOLE, ENGAGING AN ELONGATED NUT TO THE THREADS OF THE PLUG STEM, DRAWING THE PLUG DISC AGAINST THE HOLDING PLATE AND BOTTOMING THE NUT AGAINST THE WALO AT THE JUNCTURE OF THE TWO DIAMETER LENGTHS OF THE TRANSVERSE HOLE, PLACING THE PLATE IN AN ELECTROPLATING BATH AND ELECTROPLATING THE EXPOSED PORTIONS OF SAID PLUG. 